1. Field of Invention
The present invention relates to phase detection for binary signal tracking loops.
2. Description of the Prior Art
In phase detection for binary signal tracking loops, two bandpass detectors were used, one of which receives an incoming signal modulated by a local digital reference signal, known as an early code, with pulses occurring slightly earlier in time than the desired tracking signal, and the other of which receives an incoming signal modulated by a local digital reference signal, termed a late code, with pulses occurring slightly later in time than the desired tracking signal. The two bandpass detectors derived error signals which were summed to control a voltage-controlled oscillator (VCO) to ensure synchronism. However, equal gain levels in both bandpass detectors was difficult to achieve and maintain, with gain imbalance introducing improper changes in the level of the error signal. Further, direct current offset or drift in either detector compounded the problem.
In an effort to reduce the effect of gain imbalance between bandpass detectors, another type of detector, known as a "tau-dither" loop, time-shared a single bandpass detector between two channels to reduce the effects of gain drift and offset drift. However, time-sharing of a single bandpass detector reduced the effective processing time for each channel by fifty percent, causing a degradation of tracking performance, particularly where the incoming signal had a low signal-to-noise ratio.